14 



have furnished species that nndoubtedly beloug to that period, of which 

 the following is a list: 



Cha'tetes lycoperdon Say, Silver Caiion, Nevada. 



Zaphrentis f Silver City, New Mexico. 



Favosites f Silver City and Upper Miembres ^Mining Camp, New 



Mexico. 



Favistella stellata Hall, Silver City, New Mexico. 



Leptoena sericea Sowerby?, Silver City, New Mexico. 



Stropliomena plamimbona Hall, Silver City, New Mexico. 



Orthis hiforata Schlotbeim, Silver City, New Mexico. 



Orthis occidentaUs Hall, Silver City, New Mexico. 



Orthis testudinaria Dalmau % Silver City, New Mexico. 



Orthis plicateUa Hall?, Fossil Butte, near Hico, Nevada. 



Modiolopsis ? Upper Miembres Mining Camp, New Mexico. 



MacJureu ? head of Amargosa Desert, Nevada (not in situ). 



Euomphalus trochiscus Meek, Ewell's Spring, Arizona (lower horizon). 

 And also the following new species of Rhynchonella : 



Genus Rhynchonella Fischer. 



Rhynchonella argenturbica {sp. nov.) — Shell rather below me- 

 dium size, compact, subtrihedral in outline; length and width nearly 

 equal ; maximum height in old shells nearly equaling the width ; pos- 

 tero-lateral margins somewhat straightened or slightly convex; rostral 

 angle from forty to forty-five degrees; antero-lateral margins rounded; 

 front sinuous or truncate, as seen by either dorsal or ventral view. Dor- 

 sal valve more convex than the ventral, abruptly arching to the beak, 

 which is strongly incurved; mesial fold very prominent, distinctly 

 defined back to the nmbonal region, divided into either three or four 

 promment, angular, or sharply-rounded plications; sides regularly arch- 

 ing to the margins both transversely and longitudinally, but become 

 somewhat laterally flattened near the beak ; each marked by from five to 

 seven plications; those nearest the mesial fold being of about the same 

 size as those upon it, but they become smaller toward, and obsolete 

 upon, the posterolateral margins. 



Ventral valve less strongly arched than the other ; beak prominent ; 

 mesial sinus deep, occupying about one-half the width of the shell at the 

 front margin ; its sides abrupt, and the bottom having either two or three 

 lilications like those of the dorsal fold ; sides sloping away from the 

 edges of the sinus with less convexity than the sides of the dorsal valve 

 have, and become laterally compressed ne;u* the beak; plications about 

 seven on each side, becoming smaller toward, and finally obsolete 

 upon, the posterolateral spaces. 



Besides the plications, which are continued to the beaks, the surface 

 is marked by lines of growth, which are most prominent upon the plica- 

 tions, giving them a delicate cancellated appearance on some shells. 



Length and breadth, about one centimeter ; height, about eight milli- 

 ^jieters. 



Position and locality. — Strata of the age of the Cincinnati group. 

 Silver City and Upper Miembres Mining Camp, New Mexico. 



